Perusing the release notes for the latest Linksys WRT120N firmware, one of the more interesting comments reads:
Firmware 1.0.07 (Build 01) - Encrypts the configuration file.
Having previouslyreversedtheir firmware obfuscation andpatchedtheir code to re-enable JTAG debugging, I thought that surely I would be able to use this access to reverse this new encryption algorithm used to secure their backup configuration files.
Boy was I giving them way too much credit.
Here’s a diff of two backup configuration files from the WRT120N. The only change made between backups was that the administrator password was changed from “admin” in backup_config_1.bin to “aa” in backup_config_2.bin:
OFFSET backup_config_1.bin backup_config_2.bin ---------------------------------------------------------------------------------------- 0x00001468 9E 9B 92 96 91 FF FF FF |........| / 9E 9E FF FF FF FF FF FF |........|Two things to note here:
The first letter of each password (“a”) is encrypted to the same value (0x9E)The same letter (“a”) is encrypted to the same value (0x9E), regardless of its position in the passwordI immediately suspected some sort of simple single-byte XOR encryption. If true, then XORing the known plain text (“a”, aka, 0×61) with the known cipher text (0x9E) should produce the XOR key:
0x61 ^ 0x9E = 0xFFApplying the XOR key of 0xFF to the other characters in the password gives us:
0x9E ^ 0xFF = a 0x9B ^ 0xFF = d 0x92 ^ 0xFF = m 0x96 ^ 0xFF = i 0x91 ^ 0xFF = nAnd XORing every byte in the config file with 0xFF gives us a decrypted config file:
00000000 33 34 35 36 00 01 df 60 00 00 46 ec 76 31 2e 30 |3456...`..F.v1.0| 00000010 2e 30 37 00 00 00 00 00 00 00 00 00 00 00 00 00 |.07.............| 00000020 00 00 00 00 00 00 00 00 00 00 00 00 57 52 54 31 |............WRT1| 00000030 32 30 4e 00 00 00 00 00 00 00 00 00 00 00 00 00 |20N.............| 00000040 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000080 61 64 6d 69 6e 00 00 00 00 00 00 00 00 00 00 00 |admin...........| 00000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| 000000a0 00 00 00 00 00 00 00 00 61 64 6d 69 6e 00 00 00 |........admin...| 000000b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000100 00 00 00 00 00 00 00 00 30 2e 30 2e 30 2e 30 00 |........0.0.0.0.| 00000110 00 00 00 00 00 00 00 00 01 01 01 00 00 00 00 01 |................| 00000120 00 00 00 01 00 00 00 00 00 00 00 08 32 39 34 38 |............2948| 00000130 33 31 30 35 00 01 00 00 00 31 39 32 2e 31 36 38 |3105.....192.168| 00000140 2e 31 2e 31 00 00 00 00 00 32 35转载于:https://www.cnblogs.com/nightnine/p/5157208.html
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